Having 11 Bit resolution is already quite good from an simple R2R chain at the FPGA. For me it looks surprisingly good. Medium grade DDS chips like the AD9850 only use an 10 Bit ADC, though they use a longer table (e.g. 4096 points). With just 2048 points for a period, there is limited use of more than 10 Bit resolution though.

The staircase like waveform with quite some ringing suggests that there is no good reconstruction filter. So one can expect quite some high frequency images. The fast output amplifier also has some disadvantages here.

Some jitter in the square wave is normal for directly generating the square from the FPGA.

thank you for your answer, our Waveform vertical resolution is 12 bit, 4096 points, and waveform is about 2048 points . so at x-2048 points, y-4096 points, at this coordinate system, it show our waveform. For R2R , it is not easy to design, because it is hard to design, so many DDS don't use this way, if it is design better , it will be more stable than chiop way.

The jitter should not depend on the H/L ratio. It should be just a question of the 5 ns time raster. So it depends on the frequency too. This might even be the worst aspect of it. At frequencies that don't have a period that is an integer multiple of 5 ns will show the jitter. So more like low jitter only at a few special good frequencies.

This generator does not have jitter at non-multiple frequencies, unlike other budget DDS.

The jitter should not depend on the H/L ratio. It should be just a question of the 5 ns time raster. So it depends on the frequency too. This might even be the worst aspect of it. At frequencies that don't have a period that is an integer multiple of 5 ns will show the jitter. So more like low jitter only at a few special good frequencies.

This generator does not have jitter at non-multiple frequencies, unlike other budget DDS.

at square wave, our wave is not jitter . this is my advantage. so you have JDS6600, you can check

The jitter should not depend on the H/L ratio. It should be just a question of the 5 ns time raster. So it depends on the frequency too. This might even be the worst aspect of it. At frequencies that don't have a period that is an integer multiple of 5 ns will show the jitter. So more like low jitter only at a few special good frequencies.

Depending on how frequency calibration is done the good frequencies can be slightly different, depending on the exact quartz frequency. In principle they could use a different frequency scale - allowing only good ones (e.g. divider) and maybe warn about poor ones.

A special DAC chip is generally better than using just a resistor chain at the FPGA output. Most DACs do not offer that much of isolation between the digital side and analog output. So noise is in both cases a question of a good layout. This is still a low cost generator - so the cheap resistor ladder DAC is a kind of compromise.

The failure is to label it 14 Bit resolution if they actually only get 11 Bits.

The Resistor chain looks like 8 Bit R2R and 14 or 15 resistors thermometer style. So at best they could get something like 12 Bit resolution. Still I am surprised how good it seemed to work. If not careful, even at 8 Bits R2R one can get significant errors. One sees that with other low cost generators that call for 8 or 12 Bit resolution and only deliver 6-7. With an actual 11 Bit resolution it is already a big step forward.

Using true 14 or maybe just 12 Bit DACs is a cost factor - though they might save on the amplitude control this way.

About a resistor chain at the FPGA output, I have explain, and your explain is good and right too , for any plan, it was designed better , it will all be good. about the bit, I don't why where you find, because we write 12 bit Waveform vertical resolution , not 14bit. about the 14 bit , we have updated, but we only sell at china for now. because we need to test in china, after test, and no one find the problem, so we sell to the world. it is our rule for publishing the products. all our products have this progress. thank you for your support again

we have updated, but we only sell at china for now. because we need to test in china, after test, and no one find the problem, so we sell to the world. it is our rule for publishing the products. all our products have this progress. thank you for your support again

Form the picture it looks like the DAC is not a pure R2R chain, but more like using thermometer style for the upper bits. So maybe someone confuses the 14 I/O pins used for control with a 14 bit resolution. At least the DAC seems to work reasonably well as 11 Bit this way.

The DAC type does not have direct influence on the noise with small signals. The waveform should be generated at constant amplitude and only the following multiplier and attenuators reduce the amplitude if needed.

You can look at the delicate degree of 14bit waveform

I'm sorry to be rude, but I am a bit concerned about your posts in this thread. I think you are trying to imply from the context and content of your posts that you are a mere consumer who has tried the Rui-Deng model and a FeelTech model function generator. Your profile says you're from England.

However:

you list "feeltech" in your profile

your username is typical of the email addresses offered primarily to Chinese users by Tencent

a google search for that username reveals other posts in Chinese in various technical forums

your English, while adequate, leads me to believe you speak English as a second language

FeelTech is headquartered in China, and I'm not able to find any offices in the UK

I should note that all of this is just from information you offered (your username, listing feeltech in your profile) or otherwise publicly available information. And I don't know of any reason or rule that one's profile must be correct on this forum, so I doubt you've done anything wrong. I suppose I could believe that you are an Chinese expat living in the UK.

In any case, if you do work for Feeltech (and perhaps if you designed the product you are discussing) I think you should be up front and honest about that fact. After all, who else would be better qualified to analyze the properties of a modern cheap function generator than a person who just designed a modern cheap function generator?

Thanks.

First of all, I am a Chinese, I did not deliberately hide my nationality, I and everyone like FeelTech users, which is me in the "forum" learning reasons, because here you can get more technical articles, out of By chance, I saw RD Tech in the forum to promote FeelTech product designers are their students, so I will call to FeelTecH confirmation. Got FeelTecH designer Sun Yi Jie negative answer. At the request of Sun Yi Jie, I made a comparison of the FY6600 and JDSS6600, responded to the "Forum"

Can these problems be fixed in software and can user update the firmware themselves?

Or is this more a hardware-issue? How can customers tell the difference between the updated and non-updated devices?

there are two small problem, 1, background noise, it was caused by DC power supply. it is small and it doesn't affect normal using , I can make sure2, at low frequency for square wave form, when you amplify 1000 times, you will find that there is little no sync. this don't affect normal using . excep those , otheres are not my problem. because those are small problem and don't affect normal using , so we gradually update those things. now we have already update 2 problem, if you order now thank you for your concernhave a nice day

Okay, good to know. But is there a possibility to install new Firmware via USB, or can the Firmware only be updated by programming the microcontroller via the JTAG-Header?

If the latter is the case, I'd suggest that this feature is implemented as soon as possible, as it will add significant value to the instrument. If any problem is discovered that can be corrected with a firmware-update, users can just update to the new firmware instead of buying a new unit or living with that problem. It also allows you to add features later, maybe as paid options, further adding value.

Okay, good to know. But is there a possibility to install new Firmware via USB, or can the Firmware only be updated by programming the microcontroller via the JTAG-Header?

If the latter is the case, I'd suggest that this feature is implemented as soon as possible, as it will add significant value to the instrument. If any problem is discovered that can be corrected with a firmware-update, users can just update to the new firmware instead of buying a new unit or living with that problem. It also allows you to add features later, maybe as paid options, further adding value.

Thank you for your reply , friend in fact , those are no problem. it don't affect our using totally. we only say it is not perfect, because there is no perfect thing in the world. those thing are just like there is small dot on shell of a device , those don't affect normal using totally, useless you use a magnifying glass to see , you can see this dot. but we are trying to make it perfect .. thank you about the modulating the signal , we don't have this function, because this is a just DDS signal generator .. thank you again . hope you understansd what I said